Photomask and semiconductor structure

ABSTRACT

Provided is a semiconductor structure. The semiconductor structure is formed on a substrate, and includes a first region and a second region surrounded by the first region. The first region has a first pattern density, and the second region has a second pattern density. The first pattern density is smaller than the second pattern density. The second region includes a central region and a boundary region. The central region has a first critical dimension, and the boundary region has a second critical dimension. Variation between the first critical dimension and the second critical dimension is smaller than 6.5%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a photomask and a semiconductor structure.

2. Description of Related Art

As the critical dimension (CD) of semiconductor structures continues tobe reduced, the requirement on the resolution of photolithography alsobecomes higher. Generally speaking, there is usually a high patterndensity device region (e.g. memory cell region or array region) and alow pattern density device region (e.g. peripheral region). In aboundary region of the high pattern density device region, which isclose to the low pattern density device region, holes in uneven sizesand even blind hole defects of the semiconductor structure are commonlyproduced due to a significant difference in pattern density. As aresult, the product reliability is reduced. Thus, how to improve theuniformity of critical dimension in the boundary region and reduce thedefects and blind holes in the semiconductor structure, therebyimproving the product reliability, has become an important issue.

SUMMARY OF THE INVENTION

The invention provides a photomask and a semiconductor structure capableof improving uniformity of critical dimension of the photomask and thesemiconductor structure.

The invention provides a semiconductor structure capable of reducingholes in uneven sizes and blind holes in the boundary region.

The invention provides a semiconductor structure adapted for structuresof contact hole (C/H), line/space (L/S), iso trench, and iso line.

The invention provides a semiconductor structure formed on a substrate.The semiconductor structure includes a first region and a second region.The first region has a first pattern density. The second region has asecond pattern density, wherein the first region surrounds the secondregion, and the first pattern density is smaller than the second patterndensity, the second region includes a central region and a boundaryregion. The central region has a first critical dimension. The boundaryregion has a second critical dimension, wherein variation between thefirst critical dimension and the second critical dimension is less than6.5%.

According to an embodiment of the invention, there is a distance rangingfrom 0.012 μm to 0.12 μm between the first region and the second region.

According to an embodiment of the invention, a width of the first regionis at least 350 μm.

According to an embodiment of the invention, the second region is amemory cell array region, a memory cell region or an array region.

According to an embodiment of the invention, the second region is amemory cell array region, and a length of each pattern in the memorycell array region is from 36 nm to 120 nm, and a width thereof is from36 nm to 120 nm.

According to an embodiment of the invention, a pitch of each pattern inthe memory cell array region is from 76 nm to 240 nm.

According to an embodiment of the invention, the second region includesat least one pattern.

According to an embodiment of the invention, the at least one patternincludes an opening, a line, a sheet, or a combination thereof.

The invention provides a photomask, including a transparent substrateand a shielding layer. The shielding layer is located on the transparentsubstrate. The shielding layer includes a first region and a secondregion. The first region has a plurality of sub-resolution assistfeatures (SRAF). The second region has a plurality of main patterns. Thefirst region surrounds the second region, and a width of the firstregion is at least 1400 μm.

According to an embodiment of the invention, the second region includesa central region and a boundary region. The central region has a firstcritical dimension. The boundary region has a second critical dimension.Variation between the first critical dimension and the second criticaldimension is less than 1.7%.

According to an embodiment of the invention, there is a distance rangingfrom 0.048 μm to 0.48 μm between the first region and the second region.

According to an embodiment of the invention, the second region is amemory cell array region, a memory cell region or an array region.

According to an embodiment of the invention, in the memory cell arrayregion, a length of each pattern is from 144 nm to 480 nm, and a widththereof is from 144 nm to 480 nm.

According to an embodiment of the invention, a pitch of each pattern inthe memory cell array region is from 304 nm to 960 nm.

According to an embodiment of the invention, the main patterns includeat least one pattern.

According to an embodiment of the invention, the at least one patternincludes a square shape, a rectangular shape, a line shape, or acombination thereof.

According to an embodiment of the invention, the sub-resolution assistfeatures (SRAF) include a square shape, a rectangular shape, or a lineshape.

According to an embodiment of the invention, the sub-resolution assistfeatures (SRAF) are not imaged on a substrate after exposure anddevelopment processes.

According to an embodiment of the invention, a line width of eachsub-resolution assist features (SRAF) is from 60 nm to 200 nm.

According to an embodiment of the invention, an angle included betweenan arrangement direction of the sub-resolution assist features (SRAF)and an arrangement direction of the main patterns is from 0 to 180degrees.

Based on the above, the photomask of the invention uses the plurality ofsub-resolution assist features (SRAF) surrounding the plurality of mainpatterns to improve the uniformity of critical dimension between thecentral region and the boundary region of the plurality of main patternsand reduces production of defects and blind holes in the boundaryregion.

In order to make the aforementioned and other features and advantages ofthe invention comprehensible, several exemplary embodiments accompaniedwith figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1A is schematic view illustrating a photomask according to anembodiment of the invention.

FIG. 1B is a partial enlarged view of main patterns of a second regionshown in FIG. 1A.

FIG. 1C is a partial enlarged view of sub-resolution assist features(SRAF) in a first region shown in FIG. 1A.

FIG. 2 is a top view illustrating a semiconductor structure formed byusing the photomask shown in FIG. 1A according to an embodiment of theinvention.

FIG. 3 is a diagram illustrating values of critical dimension of mainpatterns in a photomask of Comparative Example 1 from a corner of aboundary region to a central region.

FIG. 4 is a diagram illustrating values of critical dimension of mainpatterns in a photomask of Experimental Example 1 of the invention froma corner of a boundary region to a central region.

FIG. 5 is a diagram illustrating values of critical dimension of asemiconductor structure of Comparative Example 2 from a corner of asubstrate boundary region to a central region.

FIG. 6 is a diagram illustrating values of critical dimension of asemiconductor structure of Experimental Example 2 of the invention froma corner of a substrate boundary region to a central region.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 1A is schematic view illustrating a photomask according to anembodiment of the invention. FIG. 2 is a top view illustrating asemiconductor structure formed by using the photomask shown in FIG. 1Aaccording to an embodiment of the invention.

Referring to FIG. 1A, a photomask 10 of this embodiment of the inventionincludes a transparent substrate 100 and a shielding layer 102. Thetransparent substrate 100 may be glass, polymer, or other suitabletransparent materials, for example. In this embodiment, a size ofpatterns of the photomask 10 is four times of a size of patterns to betransferred. Therefore, compared with a distance, pattern and size of asemiconductor structure 20 shown in FIG. 2, a distance, pattern and sizeof the photomask 10 is enlarged by four times. However, the invention isnot limited thereto. In other embodiments, the distance, pattern andsize of the photomask 10 may also be enlarged by one time, five times,or ten times, etc., for example.

The shielding layer 102 is located on the transparent substrate 100. Inan embodiment, a material of the shielding layer 102 may be metal, suchas Chrome (Cr) or other suitable materials, for example. The shieldinglayer 102 may be formed by depositing a shielding material layer bychemical vapor deposition or physical vapor deposition, and thenpatterning the shielding material layer. The chemical vapor depositionis plasma enhanced chemical vapor deposition (PECVD), low pressurechemical vapor deposition (LPCVD), etc., for example, and the physicalvapor deposition is evaporation, sputtering, ion beam deposition, etc.,for example.

The shielding layer 102 includes a first region 110 and a second region120 surrounded by the first region 110. The second region 120 is amemory cell array region, a memory cell region or an array region, forexample. In an embodiment, a distance D1 between the first region 110and the second region 120 is from 0.048 μm to 0.48 μm, for example. Inthe first region 110, the shielding layer 102 has a plurality ofsub-resolution assist features (SRAF) 104. In the second region 120, theshielding layer 102 has a plurality of main patterns 106.

The second region 120 includes a central region 130 and a boundaryregion 140 surrounding the central region 130. A critical dimension ofthe main pattern 106 in the central region 130 is CD1, and a criticaldimension of the main pattern 106 in the boundary region 140 is CD2. Ifthe second region 120 is a memory cell array region, the criticaldimension CD1 and the critical dimension CD2 should, in theory, beclose. However, when there is an overly significant difference inpattern density between the first region 110 and the second region 120,thereby generating a loading effect, variation between the criticaldimension CD1 of the main pattern 106 in the central region 130 and thecritical dimension CD2 of the main pattern 106 in the boundary region140 increases.

In the photomask 10 of this embodiment of the invention, the pluralityof sub-resolution assist features (SRAF) 104 are disposed in the firstregion 110 to reduce the loading effect in the first region 110 and thesecond region 120, thereby improving uniformity of critical dimension ofpatterns formed on a substrate 200 (FIG. 2) after a photolithographyprocess and an etching process. For example, when the plurality ofsub-resolution assist features (SRAF) 104 are not disposed in the firstregion 110, variation between the critical dimension CD1 of the mainpattern 106 of the central region 130 and the critical dimension CD2 ofthe main pattern 106 of the boundary region 140 is 2.5%. When theplurality of sub-resolution assist features (SRAF) 104 are disposed inthe first region 110 and a width R_(w) 1 of the first region 110 is atleast 1400 μm, the variation between the critical dimension CD1 of themain pattern 106 of the central region 130 and the critical dimensionCD2 of the main pattern 106 of the boundary region 140 may be less than1.7%. The variation described herein takes a process specification ofthe main patterns 106 of the central region 130 into consideration. Ingeneral, if the process specification is not considered, the criticaldimension CD1 of the main pattern 106 of the central region 130 and thecritical dimension CD2 of the main pattern 106 of the boundary region140 in this embodiment may be the same.

Referring to FIG. 1A and FIG. 2, the sub-resolution assist features(SRAF) 104 in the first region 110 cannot be imaged on the substrate 200after subsequent exposure and development processes. However, the mainpatterns 106 in the second region 120 are imaged on the substrate 200.In an embodiment, regions in the sub-resolution assist features (SRAF)104 and the main patterns 106 are light-transmissive regions, while restof the photomask 10 is an opaque region. However, the embodiments of theinvention are not limited thereto. In another embodiment, it is alsopossible that the regions in the sub-resolution assist features (SRAF)104 and the main patterns 106 are opaque regions, while the rest of thephotomask 10 is a light-transmissive region. A line width designed forthe sub-resolution assist features (SRAF) 104 small enough that thesub-resolution assist features (SRAF) 104 are not imaged on thesubstrate 200 after the subsequent exposure and development processes.

FIG. 1B is a partial enlarged view of main patterns of a second regionshown in FIG. 1A. FIG. 1C is a partial enlarged view of sub-resolutionassist features (SRAF) in a first region shown in FIG. 1A.

Referring to FIG. 1B, the main patterns 106 in the second region 120 mayinclude at least one pattern. The at least one pattern may be a line, asheet or an opening, for example. The opening may be a trench, a contacthole or a via hole. The at least one pattern may be in a shape ofsquare, rectangle, line, or a combination thereof. In an embodiment, thesecond region 120 is a memory cell array region, for example. The mainpatterns 106 are openings, for example, and a length L of each openingpattern is from 144 nm to 480 nm, a width W thereof is from 144 nm to480 nm, and a pitch P thereof is from 304 nm to 960 nm. However, theembodiments of the invention are not limited thereto.

As described above, since the size of the patterns of the photomask 10in this embodiment is four times of the size of the patterns to betransferred, after the main patterns 106 of the photomask 10 aretransferred to the semiconductor structure 20 shown in FIG. 2, a lengthof each main pattern 206 is from 36 nm to 120 nm, a width thereof isfrom 36 nm to 120 nm, and a pitch of each pattern is from 76 nm to 240nm.

Referring to FIG. 1C, in an embodiment, the sub-resolution assistfeatures (SRAF) 104 of the first region 110 include at least onepattern. The at least one pattern may be a line or an opening, forexample. The at least one pattern may be in a shape of square,rectangle, line, or a combination thereof In FIG. 1C, the sub-resolutionassist features (SRAF) 104 are openings, and a line width LW of eachopening is from 60 nm to 200 nm. Moreover, in an embodiment, an angleincluded between an arrangement direction of the sub-resolution assistfeatures (SRAF) 104 and an arrangement direction of the main patterns106 may be an arbitrary angle from 0 to 180 degrees. For example, in anembodiment, the main patterns 106 are rectangular or square openings,and the sub-resolution assist features (SRAF) 104 are line-shapedopenings. When a first direction along long sides of the rectangularopenings of the main patterns 106 is parallel to a second directionalong long sides of the line-shaped openings of the sub-resolutionassist features (SRAF) 104, the angle included between the arrangementdirection of the sub-resolution assist features (SRAF) 104 and thearrangement direction of the main patterns 106 is 0 degrees. However, ifthe first direction along the long sides of the rectangular openings ofthe main patterns 106 and the second direction along the long sides ofthe line-shaped openings of the sub-resolution assist features (SRAF)104 are perpendicular to each other, the angle included between thearrangement direction of the sub-resolution assist features (SRAF) 104and the arrangement direction of the main patterns 106 is 90 degrees.

FIG. 2 is a top view illustrating a semiconductor structure formed byusing the photomask shown in FIG. 1A according to an embodiment of theinvention.

Referring to FIG. 2, the semiconductor structure 20 is formed on thesubstrate 200 by performing the photolithography and etching processesto the substrate 200 using the photomask 10 (FIG. 1A) of the inventionas a mask. The substrate 200 is a semiconductor substrate, asemiconductor compound substrate, or a semiconductor over insulator(SOI) substrate, for example. The semiconductor may be atoms of IVAGroup, such as silicon or germanium, for example. The semiconductorcompound is a semiconductor compound formed by atoms of IVA Group, suchas silicon carbide or silicon germanium, for example, or a semiconductorcompound formed by atoms of IIIA Group or atoms of VA Group, such asgallium arsenide, for example.

The semiconductor structure 20 includes a first region 210 and a secondregion 220. The first region 210 surrounds the second region 220. In anembodiment, a distance D2 between the first region 210 and the secondregion 220 is from 0.012 μm to 0.12 μm. The first region 210 has a firstpattern density, and the second region 220 has a second pattern density.The first pattern density is smaller than the second pattern density.The second region 220 includes a central region 230 and a boundaryregion 240. A component in the central region 230 has a criticaldimension CD3. A component in the boundary region 240 has a criticaldimension CD4. The second region 220 is a memory cell array region, amemory cell region or an array region, for example. Patterns in thesecond region 220 may include at least one pattern. The at least onepattern may include an opening, a line, a sheet, or a combinationthereof.

In the conventional technology, the first pattern density of the firstregion 210 is smaller than the second pattern density of the secondregion 220, which results in greater variation between the criticaldimension CD3 of the central region 230 and the critical dimension CD4of the boundary region 240. However, referring to FIGS. 1A and 2, inthis embodiment of the invention, after performing the photolithographyand etching processes to the substrate 200 using the photomask 10 (wherethe plurality of sub-resolution assist features (SRAF) 104 are disposedsurround the plurality of main patterns 106) as a mask, a loading effectbetween the first region 210 and the second 220 may be reduced, therebyimproving uniformity of the critical dimension CD3 of the central region230 of the second region 220 and the critical dimension CD4 of theboundary region 240 of the second region 220. In an example, when thewidth R_(w) 1 of the first region 110 of the photomask 10 shown in FIG.1A of the invention is 1400 μm, the variation between the criticaldimension CD3 of the central region 230 and the critical dimension CD4of the boundary region 240 may be less than 6.5% after performing thephotolithography process and the etching process to the substrate 200.For the semiconductor structure formed without disposing thesub-resolution assist features (SRAF) in the conventional technology,the variation between the critical dimension of the central region andthe critical dimension of the boundary region thereof is approximately20%. However, in the embodiments of the invention, the variation betweenthe critical dimension CD3 of the central region 230 of thesemiconductor structure 20 and the critical dimension CD4 of theboundary region 240 of the semiconductor structure 20 may be less than6.5%. Therefore, the embodiments of the invention have more preferableuniformity of critical dimension of the patterns in the semiconductorstructure 20. In an embodiment of the invention, a width Rw2 of thefirst region 210 of the semiconductor structure 20 shown in FIG. 2 ofthe invention is 350 μm. It should be understood that the variationdescribed herein takes the process specification into consideration. Ingeneral, if the process specification is not considered, the criticaldimension CD3 of the main pattern 206 of the central region 230 and thecritical dimension CD4 of the main pattern 206 of the boundary region240 in the semiconductor structure 20 of this embodiment may be thesame.

Besides, when the variation between the critical dimension CD1 and thecritical dimension CD2 of the photomask 10 according to this embodimentof the invention is reduced, the variation between the criticaldimension CD3 and the critical dimension CD4 of the semiconductorstructure 20 of this embodiment of the invention is reduced as well.Therefore, the uniformity between the critical dimension CD3 and thecritical dimension CD4 of the boundary region 240 may be improved,thereby further reducing production of defects and blind holes in aboundary region 240 between the first region 210 and the second region220.

FIG. 3 is a diagram illustrating variation in critical dimension of mainpatterns in a photomask of Comparative Example 1 from a corner of aboundary region to a central region. In Comparative Example 1, only thesecond region has a plurality of main patterns, and the first regiondoes not have sub-resolution assist features (SRAF). FIG. 4 is a diagramillustrating variation in critical dimension of main patterns in aphotomask of Experimental Example 1 of the invention from a corner of aboundary region to a central region. A second region of the photomask ofExperimental

Example 1 has a plurality of main patterns, and a first regionsurrounding the second region has a plurality of sub-resolution assistfeatures (SRAF). In addition, a width of the first region having theplurality of sub-resolution assist features (SRAF) is 500 μm.

Based on the results shown in FIG. 3, in Comparative Example 1, when thesecond region is a memory cell array region, and a critical dimension ofeach pattern is 244×232 nm, curves close to the boundary region aresteeper and the variation in critical dimension between the boundaryregion and the central region of the photomask is approximately 2 nm to3 nm. On the other hand, based on the results shown in FIG. 4, curvesindicating the critical dimensions of the boundary region and thecentral region of the photomask in Experimental Example 1 are flatter,indicating that there is no substantial difference in critical dimensionbetween the boundary region and the central region of the photomask. Itis clearly shown that the variation in critical dimension between theboundary region and the central region of the photomask is greater inComparative Example 1, while the uniformity of critical dimensionbetween the boundary region and the central region of the photomask inExperimental Example 2 is more preferable.

In another Experimental Example, a target critical dimension (targetMCD) on a horizontal axis (X direction) in the photomask is 244 nm, andthe target critical dimension on a vertical axis (Y direction) in thephotomask is 232 nm. When the plurality of sub-resolution assistfeatures (SRAF) are not disposed in the first region of the photomask,an actual critical dimension on the horizontal axis (X direction) in thesecond region is from 246.6 nm to 242.1 nm (i.e. variation of the actualcritical dimension with respect to the target critical dimension is 4.5nm), the actual critical dimension on the vertical axis (Y direction) inthe second region is from 234.5 nm to 229.3 nm (i.e. the variation ofthe actual critical dimension with respect to the target criticaldimension is 5.2 nm), and the pattern density in the second region is23.2%. However, when the plurality of sub-resolution assist features(SRAF) are disposed in the first region of the photomask, the actualcritical dimension on the horizontal axis (X direction) in the secondregion is from 247.2 nm to 243.7 nm (i.e. the variation of the actualcritical dimension with respect to the target critical dimension is 3.5nm), and the actual critical dimension on the vertical axis (Ydirection) in the second region is 235.3 nm to 231.7 nm (i.e. thevariation of the actual critical dimension with respect to the targetcritical dimension is 3.6 nm), and the pattern density in the secondregion is 30.4%. It can be seen that the range of the mask criticaldimension (MCD) in the second region is improved to 3.6 nm from 5.2 nmwhen the mask pattern density in the second region is increased to 30.4%from 23.2% by disposing the plurality of sub-resolution assist features(SRAF) surrounding the plurality of main patterns in the photomask ofthe invention. Therefore, by using the photomask of the invention, notonly the uniformity in the second region is improved, but the patterndensity in the second region is also increased. As a result, theintegration of the device is increased.

FIG. 5 is a diagram illustrating variation in critical dimension of asemiconductor structure of Comparative Example 2 from a corner of asubstrate boundary region to a central region. The semiconductorstructure is formed on the substrate after performing thephotolithography and etching processes using the photomask ofComparative Example 1 as a mask. FIG. 6 is a diagram illustratingvariation in critical dimension of a semiconductor structure ofExperimental Example 2 of the invention from a corner of a substrateboundary region to a central region. The semiconductor structure isformed on the substrate after performing the photolithography andetching processes using the photomask of Experimental Example 1 as amask.

Based on the results shown in FIG. 5, in Comparative Example 2, when thesecond region is a memory cell array region, and a critical dimension ofeach pattern is 46×43 nm, the variation in critical dimension betweenthe boundary region and the central region of the semiconductorstructure is approximately 4 nm to 6 nm. Clearly, curves indicating theboundary region are steeper, and the variation is very significant. Onthe other hand, curves indicating the critical dimensions of theboundary region and the central region of the semiconductor structure ofExperimental Example 2 are flatter, indicating that there is nosubstantial difference in critical dimension between the boundary regionand the central region. It is clearly shown that the variation incritical dimension between components in the boundary region and thecentral region is greater in Comparative Example 2, while the uniformityof critical dimension between the components in the boundary region andthe central region is more preferable in Experimental Example 2.

In view of foregoing, the plurality of sub-resolution assist features(SRAF) are disposed to surround the plurality of main patterns in thephotomask of the invention. Therefore, the loading effect between thefirst region and the second region may be reduced, thereby reducing thevariation in critical dimension between the central region and theboundary region of the second region. Then, using the photomaskaccording to the embodiments of the invention as a mask, thephotolithography and etching processes are performed, such that thevariation in critical dimension between the central region and theboundary region in the second region of the semiconductor structure isless than 6.5%. Thus, the invention not only improves the uniformity ofcritical dimension of the photomask and semiconductor structure, butalso reduces production of defects and blind holes in the boundaryregion of the semiconductor structure. The product reliability isconsequently improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A semiconductor structure, formed on a substrate, the semiconductor structure comprising: a first region, having a first pattern density; and a second region, having a second pattern density, wherein the first region surrounds the second region, and the first pattern density is smaller than the second pattern density, wherein the second region comprises: a central region, having a first critical dimension; and a boundary region, having a second critical dimension, wherein variation between the first critical dimension and the second critical dimension is less than 6.5%.
 2. The semiconductor structure as claimed in claim 1, wherein there is a distance ranging from 0.012 μm to 0.12 μm between the first region and the second region.
 3. The semiconductor structure as claimed in claim 1, wherein a width of the first region is at least 350 μm.
 4. The semiconductor structure as claimed in claim 1, wherein the second region is a memory cell array region, a memory cell region or an array region.
 5. The semiconductor structure as claimed in claim 1, wherein the second region is a memory cell array region, and a length of each pattern in the memory cell array region is from 36 nm to 120 nm, and a width thereof is from 36 nm to 120 nm.
 6. The semiconductor structure as claimed in claim 5, wherein a pitch of each pattern in the memory cell array region is from 76 nm to 240 nm.
 7. The semiconductor structure as claimed in claim 1, wherein the second region comprises at least one pattern.
 8. The semiconductor structure as claimed in claim 7, wherein the at least one pattern comprises an opening, a line, a sheet, or a combination thereof.
 9. A photomask, comprising: a transparent substrate; and a shielding layer, located on the transparent substrate, wherein the shielding layer comprises: a first region, having a plurality of sub-resolution assist features (SRAF); and a second region, having a plurality of main patterns, wherein the first region surrounds the second region, and a width of the first region is at least 1400 μm.
 10. The photomask as claimed in claim 9, wherein the second region comprises: a central region, having a first critical dimension; and a boundary region, having a second critical dimension, wherein variation between the first critical dimension and the second critical dimension is less than 1.7%.
 11. The photomask as claimed in claim 9, wherein there is a distance ranging from 0.048 μm to 0.48 μm between the first region and the second region.
 12. The photomask as claimed in claim 9, wherein the second region is a memory cell array region, a memory cell region or an array region.
 13. The photomask as claimed in claim 9, wherein the second region is a memory cell array region, a length of each pattern in the memory cell array region is from 144 nm to 480 nm, and a width thereof is from 144 nm to 480 nm.
 14. The photomask as claimed in claim 13, wherein a pitch of each pattern in the memory cell array region is from 304 nm to 960 nm.
 15. The photomask as claimed in claim 9, wherein the main patterns comprise at least one pattern.
 16. The photomask as claimed in claim 15, wherein the at least one pattern comprises a square shape, a rectangular shape, a line shape, or a combination thereof.
 17. The photomask as claimed in claim 9, wherein the sub-resolution assist features (SRAF) comprise a square shape, a rectangular shape, or a line shape.
 18. The photomask as claimed in claim 9, wherein the sub-resolution assist features (SRAF) are not imaged on a substrate after exposure and development processes.
 19. The photomask as claimed in claim 18, wherein a line width of each sub-resolution assist features (SRAF) is from 60 nm to 200 nm.
 20. The photomask as claimed in claim 9, wherein an angle included between an arrangement direction of the sub-resolution assist features (SRAF) and an arrangement direction of the main patterns is from 0 to 180 degrees. 